Optical information recording medium

ABSTRACT

An optical information recording medium includes an inorganic film which changes an intensity or an intensity distribution of light formed on an upper surface of a board, and a recording film, a protecting film, and a reflecting film formed on an upper portion of the inorganic film. The inorganic film is constructed by N (N is an integer of 2 or more) kinds of phases, the phases of the kinds within a range from at least one or more kinds to (N−1) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases. Information, consequently, may be written in high density.

TECHNICAL FIELD

The invention relates to an optical information recording medium and,more particularly, to an optical information recording medium which canread out or read/write at a high recording density and has highreliability for the repetitive recording and reproducing operations.

BACKGROUND ART

In an optical information recording medium, a compact disc (CD), a laserdisc (LD), or the like has been widespread. In recent years, a DVDhaving a recording density that is seven or more times as large as thatof the CD has been put into practical use. As for the DVD, developmentis being made as a rewritable recording/reproducing medium besides aread only ROM (DVD-ROM) in which information has directly been writtenon a board. The realization of the practical use of the DVD is beingexamined also as an RAM for a computer (DVD-RAM).

In a DVD, a high density recording has been accomplished by using alaser beam having a shorter wavelength of about 650 nm than that of thelaser (780 nm) used in a CD or the like. In order to handle informationof a large capacity such as computer graphics or the like, however, itis necessary to accomplish a further high recording density that is 1.5to 2 times as large as the above density. To accomplish it, developmentof semiconductor lasers of green to blue of further short wavelengths(wavelengths: 520 to 410 nm) is being made.

A super resolution film can be mentioned as another high recordingdensity technique. The super resolution film is a film which is formedon a lower surface of a recording medium and a high recording densitycan be accomplished by reducing a beam spot of incident lighttransmitted through the film.

One of mechanisms of a super resolution effect is a satural absorptionphenomenon which is a phenomenon realized by using such nonlinearoptical characteristics that the super resolution film transmits lighthaving an intensity that is equal to or larger than its saturalabsorption amount and absorbs light having an intensity below thesatural absorption amount. Since a spatial intensity of the laser beamwhich is used for reading or writing has a Gaussian distribution, whenthe beam passes through the super resolution film, the light at a bottomportion having a low intensity is absorbed by the super resolution filmand the light at a center portion having a high intensity istransmitted. Therefore, a beam diameter after the transmission can bereduced.

At present, as such a super resolution film, an organic film of thephthalocyanine system, materials (compounds) of the chalcogenide system,or the like as shown in JP-A-8-96412 or the like can be mentioned.Besides them, such a trial that, as the same organic material, athermochromic material disclosed in JP-A-6-162564 or a photochromicmaterial disclosed in JP-A-6-267078 is used as a super resolution filmis also known.

However, each of the materials as mentioned above has problems in termsof the reliability, productivity, and the like. In the organic film,since an energy density of the beam is locally very high upon recordingor reading, if the recording or reproducing operation is repetitivelyperformed, there is a fear that the film deteriorates gradually.Therefore, it is difficult to guarantee the sufficient number of timesof the recording or reproducing operation under a severe use environmentas in case of an RAM for a computer or the like. Since chalcogenide ischemically unstable, it is difficult to obtain a long guaranteeingperiod.

DISCLOSURE OF INVENTION

It is an object of the invention to obtain an optical recording mediumhaving a super resolution film which can guarantee the repetitiverecording or reproducing operation for a long period and has highproductivity and a high super resolution effect.

To solve the above problem, according to the invention, there isprovided an optical information recording medium comprising, at least: aboard on which pits having information have been formed; and a filmwhich is formed directly on the board or formed thereon through anotherlayer and changes a reflectance or an intensity distribution ofreflection light in dependence on an intensity of incident light (such afilm is hereinbelow also referred to as a super resolution film),wherein the film is inorganic materials (compounds) constructed by N(N=2, 3, 4, . . . : integer of 2 or more) kinds of phases, the phases ina range from at least one kind to (N−1) kinds among the N kinds ofphases are continuous phases, and the other phases are discontinuousphases.

The discontinuous phases are, for example, phases such as spherical orpillar fine particles and are phases having such a discontinuousstructure that they are distributed in one matrix. The continuous phasesare phases represented by such a matrix phase and are phases all ofwhich are continuous and exist not being independent. The continuousphases exist so as to disperse the discontinuous phases.

There is also provided an optical information recording mediumcomprising, at least: a board; a film which is formed directly on theboard or formed thereon through another layer and changes a reflectanceor an intensity distribution of reflection light in dependence on anintensity of incident light; and a recording film which is formeddirectly on the film or formed thereon through another layer and onwhich information is recorded by the light, wherein the film isinorganic materials (compounds) constructed by N (N=2, 3, 4, . . . :integer of 2 or more) kinds of phases, the phases in a range from atleast one kind to (N−1) kinds among the N kinds of phases are continuousphases, and the other phases are discontinuous phases. A mean diameterof the discontinuous phases lies within a range from 1 nm or more to 70nm or less. A width of continuous phases existing between thediscontinuous phases lies within a range from 0.3 nm or more to 100 nmor less. Further, the continuous phases are amorphous inorganiccompounds and the discontinuous phases are crystal inorganic compounds.The continuous phases are a dielectric substance and the discontinuousphases are any of a metal, a semiconductor, and a dielectric substance.

According to the invention, there is provided an optical informationrecording medium comprising, at least: a board on which pits havinginformation have been formed; and a film which is formed directly on theboard or formed thereon through another layer and changes a reflectanceor an intensity distribution of reflection light in dependence on anintensity of incident light, wherein the film is constructed by N (N=2,3, 4, . . . : integer of 2 or more) kinds of phases containing at leastone or more kinds of elements selected from Co, Ti, V, Cr, Mn, Fe, Ni,Si, Pb, Bi, and Al, the phases in a range from at least one kind to(N−1) kinds among the N kinds of phases are continuous phases, and theother phases are discontinuous phases.

Further, there is provided an optical information recording mediumcomprising, at least: a board; a film which is formed directly on theboard or formed thereon through another layer and changes a reflectanceor an intensity distribution of reflection light in dependence on anintensity of incident light; and a recording film which is formeddirectly on the film or formed thereon through another layer and onwhich information is recorded by the light, wherein the film isconstructed by N (N=2, 3, 4, . . . integer of 2 or more) kinds of phasescontaining at least one or more kinds of elements selected from Co, Ti,V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a range from atleast one kind to (N−1) kinds among the N kinds of phases are continuousphases, and the other phases are discontinuous phases.

Further, according to the invention, there is provided an opticalinformation recording medium comprising, at least: a board; a film whichis formed directly on the board or formed thereon through another layerand changes a reflectance or an intensity distribution of reflectionlight in dependence on an intensity of incident light; and a recordingfilm which is formed directly on the film or formed thereon throughanother layer and on which information is recorded by the light, whereina refractive index of the film changes due to the incident light whenthe incident light enters, and assuming that a refractive index at thetime when no incident light enters is labelled to n₀ and an intensity ofthe incident light is set to I, if the absolute value n of therefractive index that is measured is indicated by

n=n ₀ +n ₂ I

a value of n₂ lies within a range from 1.0×10⁻⁹ (m²/W) or larger to1.0×10⁻⁷ (m²/W) or less.

In this instance, the refractive index change (n−n₀) occurs in such amanner that the refractive index is saturated within a period of timewhich lies within a range from 2.50×10⁻⁷ second or longer to 3.50×10⁻⁷second or shorter after the irradiation of the incident light and isrecovered to the original refractive index within a time interval whichlies within a range from 2.5×10⁻⁷ second or longer to 1.0×10⁻² second orshorter after the removal of the incident light.

Further, the film is an oxide which contains a Co oxide of 60 to 95weight % as an oxide of CoO and in which a remaining part is constructedby elements of at least one or more kinds among Si, Ti, Al, Pb, and Bi.

According to the invention, there is provided an optical informationrecording/reproducing apparatus comprising, at least: lasers of aplurality of wave-lengths; means for selecting one of the lasers; and amechanism for automatically adjusting a focal point which changes everylaser, wherein the apparatus further has means for discriminating arecording capacity of a medium to record or reproduce and means forchanging a tracking in accordance with the medium discriminated by thediscriminating means.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a cross section of an ROM disk formed in anembodiment of the invention.

FIG. 2 is a diagram showing a reading frequency dependence of an outputderived from the ROM disk in FIG. 1.

FIG. 3 is a diagram showing an X-ray diffraction pattern of a superresolution film formed in the embodiment of the invention.

FIG. 4 is a diagram showing an X-ray diffraction pattern of a superresolution film formed in the embodiment of the invention.

FIG. 5 is a diagram showing an X-ray diffraction pattern of a superresolution film formed in the embodiment of the invention.

FIG. 6 is a photograph showing a TEM image of a super resolution filmformed in the embodiment of the invention.

FIG. 7 is a photograph showing an electron beam diffraction image of asuper resolution film formed in the embodiment of the invention.

FIG. 8 is a diagram of a cross section of an RAM disk formed in theembodiment of the invention.

FIG. 9 is a diagram showing a change in output for a recording marklength which is obtained from the RAM disk of FIG. 8.

FIG. 10 is a diagram showing a change in laser beam diameter in the casewhere a glass film is formed and in the case where it is not formed.

FIG. 11 is a diagram showing a relation between the number of times ofthe recording/reproducing operation and an output of the RAM disk onwhich a super resolution film in the embodiment of the invention hasbeen formed.

FIG. 12 is a diagram showing a relation between a CoO content and theoutput.

FIG. 13 is a diagram showing a relation between a mean particle diameterof particles precipitated on the film and an output.

FIG. 14 is a block diagram of an optical informationrecording/reproducing apparatus formed in the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

The invention will be described in detail by using an embodiment.

FIG. 1 shows a schematic diagram of a partial cross section of an ROMdisk formed in the embodiment. In FIG. 1, reference numeral 1 denotes aboard; 2 a super resolution film; 5 an SiO₂ protecting film; 4 areflecting film made of a material of the Al—Ti system; and 6 a pitwhich has been written with information. Although one of polycarbonate,polyolefin, glass, and the like is used as a board 1 in accordance withthe specification, polycarbonate is used in the embodiment. In FIG. 1,light for reading (for example, laser beam) enters from the lowerposition as shown by an arrow.

Further, the ROM disk is formed by the following steps. First, a pitpattern having information is formed on a photoresist by using a laser.After that, the pit pattern is copied to an Ni die and polycarbonate isinjection formed into the die, thereby forming a board. The superresolution film 2 having a desired film thickness is formed on the boardby sputtering. The SiO₂ protecting film 5 having a film thickness of 140nm is formed and, thereafter, the reflecting film 4 having a filmthickness of 100 nm made of a material of the Al—Ti system is formed bysputtering. A thickness of board 1 is equal to 0.6 mm. In theembodiment, two boards (shown in FIG. 1) formed as films are adhered toeach other with a UV (ultra-violet rays) curable resin while thereflecting films 4 are set to the back side, so that an ROM disk havinga thickness of 1.2 mm is obtained. As a film thickness of superresolution film 2, a thickness within a range from 100 nm or more to 300nm or less is selected.

In the embodiment, by changing compositions (Nos. 1 to 29 in Table 1,which will be explained hereinlater) of the film corresponding to thesuper resolution film 2, ROM disks (No. 30 in Table 1, which will beexplained hereinlater) are formed and super resolution characteristicsof each disk are evaluated. As a comparison example, an ROM disk (No. 30in Table 1, which will be explained hereinlater) on which the superresolution film 2 is not formed is also formed. A sputtering apparatuswhich can simultaneously sputter two disks is used for sputtering. Thecompositions are changed on the films by independently changing theirpowers.

FIG. 14 shows a block diagram of an optical informationrecording/reproducing apparatus used in the embodiment. The apparatushas a medium discriminating means for discriminating the kind of opticaldisk serving as an optical memory medium. An optical disk is fixedtemporarily to a rotating mechanism connected directly or indirectly toa rotary shaft of a motor which is controlled by motor circuit controlmeans. The information on the optical disk is read as a photosignal by alaser serving as a light source in the pickup and a sensing unit forsensing the reflection light. Information is stored onto the opticaldisk by the light source in the pickup. The photosignal passes through apreamplifier, read signal processing means, address reading means, andclock sync signal reading means and is outputted through reproductionsignal demodulating means to the outside of the apparatus byreproduction data sending means. Reproduction data is outputted bypredetermined output means such as display apparatus, speaker, or thelike or is subjected to data processes by an information processingapparatus such as a personal computer or the like.

In the embodiment, laser selecting means which can select an arbitrarylaser wavelength is provided besides a circuit system which is used fornormal recording and reproduction. A peak power which is used isdetermined by peak power deciding means on the basis of an output of thelaser selecting means and on the basis of an analysis of a laser powercontrol information analyzing means. A reading power is similarlydetermined by reading power deciding means. An output of the peak powerdeciding means is inputted to a laser driver via a recording power DCamplifier and an erasing power DC amplifier through power ratio decidingmeans and controls the light source in the pickup. Similarly, an outputof the reading power deciding means is inputted to the laser driverthrough a reading power DC amplifier and controls the light source inthe pickup. As an actual laser, a semiconductor laser of 780 nm which isused for a CD and semiconductor lasers of 650 nm, further, 520 nm, and410 nm which are used for a DVD are installed.

Since a focus and a focal depth differ depending on a wavelength, thelaser is designed so as to have such a structure that an auto-focusingcan be performed in association with the selection. Further, incorrespondence to a structure in which a super resolution film ismounted on the disk and a tracking width is made thin, in tracking errordetecting means, another means for high density recording is separatelyprovided, thereby enabling the tracking operation to be performed inaccordance with a medium. A kind discriminating mechanism fordiscriminating the medium by using a difference of reflectance of mediais provided, thereby designing the apparatus so that the auto-trackingcan be performed in accordance with a difference of the medium kinds.Upon data recording, recording data is inputted from recording datareceiving means, is data modulated by recording data modulating means,is inputted to the laser driver through recording timing correctingmeans, and controls the light source in the pickup.

By using a construction as shown in FIG. 14, not only conventional CDand DVD can be compatibly used but also disks having different recordingcapacities due to the realization of a large capacity can be handled byone apparatus. The optical information recording/reproducing apparatuscan be properly changing its construction in accordance with its objector application field and used.

Table 1 shows reproduction output characteristics of compositions of thefilms corresponding to the formed super resolution films and a lowfrequency component (2 MHz) and a high frequency component (10 MHz)under such conditions that a reading power is set to 1, 2, 3, and 4 mW.The presence or absence of the super resolution effect to bediscriminated from this table is also shown. The laser beam used forreading is derived from the semiconductor laser of a wavelength of 650nm.

TABLE 1 Nonlinear Output refractive Response Super Components 2 MHz 10MHz index time resolution No. (weight ratio) 1 mW 2 mW 3 mW 4 mW 1 mW 2mW 3 mW 4 mW (n₂ (m²/w) (ns) effect 1 CoO 34 35 35 33 1 2 2 1 2.5 ×10⁻¹⁵ 140 X 2 SiO₂ 38 40 41 40 1 2 2 2 3.4 × 10⁻¹⁸ 125 X 3 SiO₂:CoO =1:1 35 36 36 37 2 3 3 2 6.2 × 10⁻¹² 210 X 4 SiO₂:CoO = 1:2 43 44 45 4710 13 20 25 2.7 × 10⁻⁸ 330 ◯ 5 SiO₂:CoO = 1:3 39 40 45 42 17 19 23 285.4 × 10⁻⁸ 345 ◯ 6 SiO₂:CoO = 1:4 38 35 38 40 20 25 30 35 7.4 × 10⁻⁸ 350◯ 7 SiO₂:CoO = 1:9 38 38 39 38 22 27 32 38 1.0 × 10⁻⁷ 350 ◯ 8 Glass 3639 32 37 1 2 2 3 6.3 × 10⁻¹⁷ 180 X 9 Glass:CoO = 1:1 37 38 40 41 5 4 8 95.9 × 10⁻¹² 220 X 10 Glass:CoO = 1:2 35 38 39 38 12 15 21 29 3.3 × 10⁻⁸300 ◯ 11 Glass:CoO = 1:3 37 38 38 37 17 20 22 28 5.9 × 10⁻⁸ 320 ◯ 12Glass:CoO = 1:4 38 39 41 40 20 25 29 32 1.1 × 10⁻⁷ 350 ◯ 13 TiO₂ 35 3636 35 1 2 3 3 1.0 × 10⁻¹¹ 200 X 14 TiO₂:CoO = 1:1 37 36 35 37 2 3 4 62.9 × 10⁻¹⁰ 195 X 15 TiO₂:CoO = 1:2 35 37 38 40 15 16 18 22 9.2 × 10⁻⁹250 ◯ 16 TiO₂:CoO = 1:3 36 38 39 40 15 18 19 21 2.2 × 10⁻⁸ 310 ◯ 17TiO₂:CoO = 1:4 37 35 38 39 18 19 22 28 6.7 × 10⁻⁸ 345 ◯ 18 Al₂O₃ 39 3837 38 2 3 2 2 2.3 × 10⁻¹⁸ 155 X 19 Al₂O₃:CoO = 1:1 39 40 38 39 14 15 1820 1.0 × 10⁻⁸ 325 ◯ 20 Al₂O₃:CoO = 1:2 40 41 41 40 15 17 19 23 2.5 ×10⁻⁸ 335 ◯ 21 Al₂O₃:CoO = 1:3 35 36 38 38 17 18 20 25 1.0 × 10⁻⁸ 350 ◯22 SiO₂—PbO 35 37 37 38 10 12 13 15 9.4 × 10⁻⁹ 280 ◯ 23 (SiO₂—PbO):CoO =1:1 38 38 39 41 17 18 20 25 2.2 × 10⁻⁸ 350 ◯ 24 (SiO₂—PbO):CoO = 1:2 3938 37 38 22 25 28 30 6.5 × 10⁻⁸ 360 ◯ 25 (SiO₂—PbO):CoO = 1:4 40 41 4140 25 26 30 34 3.0 × 10⁻⁸ 345 ◯ 26 SiO₂—Bi₂O₃ 36 35 37 36 12 13 15 168.8 × 10⁻⁹ 310 ◯ 27 (SiO₂—Bi₂O₃):CoO = 1:1 37 37 38 37 18 19 22 25 6.2 ×10⁻⁸ 340 ◯ 28 (SiO₂—Bi₂O₃):CoO = 1:2 38 39 38 38 21 23 24 28 4.0 × 10⁻⁸325 ◯ 29 (SiO₂—Bi₂O₃):CoO = 1:4 37 38 36 37 20 22 23 25 2.1 × 10⁻⁸ 315 ◯30 None 38 41 43 41 1 2 3 5 2.7 × 10⁻²⁰ 120 X

In the embodiment, to obtain a higher super resolution effect, a filmcontaining the Co oxide showing large absorption at wavelengths around650 nm is used as a base and various materials are added, therebyforming films. In Table 1, compositions are shown by a weight ratio ofeach component. In Table 1, No. 1 shows a single-phase film of CoO andNo. 2 shows a single-phase film of SiO₂. Nos. 3 to 7 indicate filmsformed by using two films of SiO₂ and CoO as targets and adjusting asputtering power of each target. Similarly, No. 8 shows a film formed bymixing a soda-lime glass of the SiO₂—Na₂O—CaO—MgO—Al₂O₃ system. Nos. 9to 12 indicate films formed by mixing the soda-lime glass and CoO. No.13 indicates a TiO₂ single layer film. Nos. 14 to 17 denote mixturefilms by mixing CoO and TiO₂.

Further, Nos. 18 to 21 show mixture films of the Al₂O₃ system and CoO.Nos. 22 to 25 show mixture films of the SiO₂—PbO glass system and CoO.Nos. 26 to 29 show mixture films of a single layer film of theSiO₂—Bi₂O₃ glass system and CoO. In those glass systems, glass blocks ofthe SiO₂—PbO system and the SiO₂—Bi₂O₃ system are previously formed andused as targets, thereby forming the films. No. 30 relates to an examplein which the super resolution film 2 is not formed.

In FIG. 2, the frequency dependence of reproduction outputcharacteristics was analyzed by a spectrum analyzer. A measurementexample of the reproduction output characteristics by the spectrumanalyzer is shown. In FIG. 2, the formed film is the film of No. 4 inthe embodiment. A measurement example in the case (No. 30) where no filmis formed is also shown as a comparison example. Both reproducing laserpowers are equal to 1 mW.

In the case where the film of No. 4 in the embodiment is formed as asuper resolution film, it has been found that an output level is high upto a higher frequency component than that in the case where no superresolution film is formed (No. 30). Since the high frequency componentof the signal is drawn on the ROM disk by a denser pit pattern, in thecase where the super resolution film is formed, this means that a finerpit pattern is read out and a reproduction signal is outputted. Thus, inthe case where the super resolution film of No. 4 is formed, the superresolution effect is obtained.

Upon discrimination of the super resolution effect in Table 1, outputsat 2 MHz and 10 MHz in each reproduction output are read out from aspectrum as shown in FIG. 2. The case where the output at 10 MHz as ahigh frequency signal is equal to or higher than 10 dB is set to “o” byregarding that there is the super resolution effect. The case where itis lower than 10 dB is determined by setting it to “x”.

In the case where the super resolution film is not formed like No. 30 inTable 1, as shown in FIG. 2, although a relatively high output isobtained at a low frequency of 2 MHz, a sufficient output is notobtained at a high frequency of 10 MHz and it has been found that datain this frequency region cannot be read out.

In the CoO—SiO₂ system of Nos. 1 to 7, reproduction outputs at a highfrequency are low and the super resolution effect cannot be obtained incase of the CoO single-phase film of No. 1 and the SiO₂ single-phasefilm of No. 2 and in the case where the (SiO₂:CoO) ratio of No. 3 isequal to (1:1). In cases of Nos. 4 to 6 in which the content of CoOexceeds 60%, the high frequency component is also reproduced as a highoutput and the super resolution effect is obtained.

In the CoO-soda-lime glass system of Nos. 8 to 12, in a manner similarto the cases of Nos. 2 to 6, although the super resolution effect cannotbe obtained in case of the glass single-phase film of No. 8 and in caseof the (glass:COO) ratio=(1:1) of No. 9, the super resolution effect canbe obtained in cases of Nos. 10 to 12 in which the CoO content is large.

Even in the TiO₂—CoO system films of Nos. 13 to 17, in a manner similarto the embodiment, although the super resolution effect cannot beobtained in case of the TiO₂ single-phase film (No. 13), the superresolution effect can be obtained in Nos. 13 to 17 in which a largeamount of CoO is contained. Similarly, in the Al₂O₃—CoO system of Nos.18 to 21, although the super resolution effect is not obtained in theAl₂O₃ single-phase film, the super resolution effect can be obtained byallowing a large amount of CoO to be contained in this film.

In the (SiO₂—PbO)—CoO system of Nos. 22 to 25 and the (SiO₂—Bi₂O₃)—CoOsystem film of Nos. 26 to 29, the super resolution effect can beobtained even in the case where CoO is not contained. It has been foundthat by allowing CoO to be contained therein, an output at a highfrequency is large and the very excellent super resolution effect isobtained.

From the above results, it has been found that the high super resolutioneffect can be obtained irrespective of the components of the matrix suchas SiO₂, glass, TiO₂, or the like if CoO of the content of about 65% ormore is contained. Therefore, a relation between the super resolutioneffect and the CoO content is examined from the output of the highfrequency component of 10 MHz at the time when SiO₂ is used as a matrixcomponent and the CoO content is increased.

FIG. 12 shows an output dependence of the ROM disk for the CoO content(weight ratio). The laser wavelength is set to 650 nm and the laseroutput is set to 2 mW. As shown in FIG. 12, it has been found that in aregion of a small CoO content, the output is equal to 1 to 2 dB and islow and the super resolution reproduction is not performed. It has beenfound that the output gradually increases from a point where the CoOcontent is equal to about 60 weight % and a relatively high output ofabout 10 to 20 dB is obtained in a range where the COO content is equalto up to 95 weight %. However, it has been found that if the CoO contentexceeds 95 weight %, the output drops suddenly and the super resolutioneffect is not obtained.

As mentioned above, to obtain the high super resolution effect, it isdesirable that the CoO content (when the Co oxide is calculated as anoxide of CoO) lies within a range from 60 weight % or more to 95 weight% or less irrespective of the kind of matrix.

As mentioned above, in the film having the high super resolutioncharacteristics, as shown in Table 1, the reflection light intensity(corresponding to the output), namely, the reflectance is largelychanged in dependence on the incident light intensity. As will beexplained hereinlater, the reflection intensity of the beam which wasreflected by the reflecting film and returned after it had beentransmitted through the film does not have a Gaussian distribution uponentering and a deviation occurs in the intensity distribution. From theabove results, it has been found that the high super resolution effectis obtained by providing the film in which the reflectance of thereflection light is changed or the intensity distribution is changed independence on the intensity of the incident light.

As shown in Table 1, the nonlinear refractive index and the responsetime of the refractive index change of each film are subsequentlyevaluated. The evaluation of those optical characteristics is made byusing a Z-scan method whereby the film is formed on a glass board, alaser beam of 650 nm is vertically inputted onto the film surface, asample is scanned in the optical path direction of the incident light,and a peak intensity of the laser is plotted. A nonlinear refractiveindex n₂ is calculated by using the following equation.

n=n ₀ +n ₂ I

where, n denotes the refractive index to be observed, n₀ indicates therefractive index which does not depend on the intensity of light, and Ishows the intensity of the incident light (W/²). Therefore, the largerthe value of n₂ is, the larger the intensity dependence of therefractive index on the light is, and the materials can be regarded asexcellent nonlinear optical materials.

The response time is evaluated by a method whereby pulse light on theorder of μ second is irradiated as an excitation light, pulse light onthe order of nanosecond is inputted as reading light, the refractiveindex is measured, and a change in refractive index in the pulse lightis plotted for the time. A time that is required from a point when theexcitation light enters until a point when the refractive index changesand is saturated is calculated and used as a response time.

By first comparing the refractive index change amount n₂, it has beenfound that n₂ of the materials by which the super resolution effectappeared lies within a range of 10⁻⁹ to 10⁻⁷. It has been also foundthat in case of the materials whose n₂ is equal to or less than9.0×10⁻¹⁰, no super resolution effect is derived. From the aboveresults, in order to obtain the super resolution effect, it is necessaryto set the nonlinear refractive index n₂ to be equal to or larger than1.0×10⁻⁹ (m²/W). If the refractive index change amount is too large,such a phenomenon that the incident light does not reach the recordingfilm appears. When it is examined in detail, if n₂ exceeds 1.0×10⁻⁵(m²/W), the incident light does not reach the recording film and cannotbe detected by the photosensing system.

By the above examination, it is preferable that the nonlinear refractiveindex n₂ lies within a range from 1.0×10⁻⁹ (m²/W) or larger to 1.0×10⁻⁵(m²/W) or less.

The faster the response time of the film is, the larger the refractiveindex change is obtained even if the medium is rotated at a high speed.It has been found that the larger the nonlinear refractive index n₂ is,the longer the response time is. Although the response time changeswithin a range from 120 nsec to 360 nsec, when the film by which thesuper resolution effect can be obtained is examined, it has been foundthat it is sufficient that the response time is equal to or shorter than350 nsec. If the response time is equal to or shorter than that value,even if the nonlinear refractive index is large, the response time isslow, so that the apparent refractive index change amount decreases. Ifthe response time is too fast contrarily, since the refractive indexsuccessively changes during the irradiation of the laser beam, therefractive index is returned to the initial value according tocircumstances. There is, consequently, a problem that the refractiveindex change amount decreases. According to the embodiment, if theresponse time is equal to or longer than 250 nsec, a decrease inrefractive index change amount does not appear. By the aboveexamination, it is desirable that the response time lies within a rangefrom 250 nsec (2.50×10⁻⁷ second) or longer to 350 nsec (3.50×10⁻⁷second) or shorter.

As for an optical information recording medium as a rotating member inwhich a disk rotates, it has been found that in the case where a portionto be irradiated has been recovered to the original refractive indexuntil the disk is rotated once, the information can be reproduced at ahigh S/N ratio. By examining the recovery time in detail, good resultsare obtained in a film which is recovered for a period of time within arange from 250 nsec or longer to 10 msec or shorter. If the recoverytime is shorter than 250 nsec, since the foregoing response time is alsoshortened in such a film, the refractive index change amountsubstantially decreases. If the recovery time exceeds 10 msec, therefractive index is not recovered until the disk is rotated once and agood super resolution effect is not obtained. From the above results, itis desirable that the recovery time lies within a range from 250 nsec(2.5×10⁻⁷ second) or longer to 10 msec (1.0×10⁻² second) or shorter.

Embodiment 2

To subsequently examine a film structure that is effective to obtain thesuper resolution effect, the film structure of each super resolutionfilm is analyzed by an X-ray diffraction, a transmission electronmicroscope, and an energy dispersive X-ray spectroscopy. In theembodiment, the film structure of No. 4 by which the super resolutioneffect was obtained and the film structure of Nos. 1 and 2 by which nosuper resolution effect was derived are analyzed.

FIG. 3 shows an X-ray diffraction pattern of the film of No. 2 as acomparison example. From this diagram, it has been found that a cleardiffraction peak does not appear in the film of No. 2 and this film isamorphous.

FIG. 4 shows an X-ray diffraction peak of the film of No. 4. As shown inFIG. 4, a peak indicative of the existence of a crystal appears while ahalopattern which is obtained from the board is used as a background.From the obtained peak, it is possible to decide that the precipitatedcrystal is CoO. To examine a fine structure of this film in detail, thefilm structure is evaluated by the transmission electron microscope.

FIG. 6 is a photograph showing a plane TEM image of the film of No. 4.As shown in the photograph of FIG. 6, it has been found that the film ofNo. 4 is a set of fine particles having a particle diameter of about 10nm. It has also been found that a grain boundary phase having a width ofabout 1 nm exists in the grain boundary portion. It has been found thatthe grain boundary phase is grown in a state to surround the particlesand the grain boundary phase itself forms mesh-like continuous phases.It has been found that the crystal particles are mutually and spatiallyseparated by the continuous phases and become the discontinuous phases.It has, therefore, been found that the film of No. 4 is inorganicmaterials (compounds) constructed by two kinds of phases, one of the twokinds of phases is the continuous phases, and the other phases are thediscontinuous phases.

A similar examination is made for the film of No. 23 in Table 1. It hasbeen found that the film of No. 23 is inorganic compounds constructed bythree kinds of phases, one kind among the three kinds of phases is thecontinuous phases containing Si, and the other two kinds of phases arethe two kinds of discontinuous phases containing Co and Pb.

Subsequently, FIG. 7 is a photograph showing a selected area electrondiffraction pattern of the film of No. 4. Many spots are observed atseveral portions of a d value in the photograph. From these results, ithas been found that the particles are crystal gain. A slightly brighthalo is observed inside of a ring constructed by those spots. Sinceamorphous constructing this halopattern is not observed in theparticles, it is possible to decide that the grain boundary phase isamorphous.

From the above results, it has been found that the film of No. 4 is aset of fine crystal gain having a mean particle diameter of about 10 nmsurrounded by the amorphous grain boundary phases.

FIG. 5 shows an X-ray diffraction pattern of the film of No. 1. As shownin the diagram, a very clear crystalline peak is observed. This peakcorresponds to CoO and Co₃O₄. When a fine structure of this film isevaluated by the TEM, a particle diameter is equal to about 0.1 μm. Theexistence of the amorphous phase as shown in the photograph of FIG. 6 isnot observed in the grain boundary portion. From the above results, ithas been found that the halopattern seen in the X-ray diffractionpattern of FIG. 5 is caused due to the glass board and the film of No. 1is constructed only by a crystal.

From the results of the fine structure analysis and the results of therecording and reproducing characteristics shown in Table 1 mentionedabove, it has been found that-the necessary super resolution effectcannot be derived if the film is the continuous phases such as perfectamorphous or the continuous phases as a perfect crystal. It has beenfound that a high super resolution effect can be obtained if the filmhas such a structure that the crystal particles (discontinuous phases)having a particle diameter on the order of nanometer are surrounded bythe amorphous continuous phases like a film of No. 4.

An influence which is exerted on the super resolution effect by theexistence state of the fine particles is subsequently examined. In theexamination, the film of No. 4 is formed as a super resolution film byusing a glass board as a board.

The particle diameter of the particles which are formed can becontrolled by controlling a board temperature upon film formation. Filmshaving various particle diameters are formed by using the aboveprinciple and the super resolution effect is examined. The examinationof the super resolution effect is made by evaluating the output of thehigh frequency component shown in FIG. 2.

FIG. 13 shows a change in output for a mean particle diameter (nm) ofthe fine particles observed in the film of No. 4. As shown in thediagram, in the case where the mean particle diameter of the fineparticles is equal to 0.8 nm, the high frequency output is notsufficiently obtained and an output level is the same as that in case ofthe amorphous. When the mean particle diameter of the fine particles isequal to 1.2 nm, the output is equal to 15 dB and is improved largely.When the mean particle diameter of the fine particles lies within arange from 5 nm or larger to 50 nm or less, the output is equal to about28 dB and a relatively large value is obtained.

It has been found that, when the mean particle diameter of the fineparticles is further increased, the output decreases from a point whereit is equal to about 60 nm and, when the mean particle diameter is equalto 70 to 90 nm, the output is reduced to a small level on the order ofone digit. It is considered that this is because as the mean particlediameter of the fine particles increases, the effect of dispersion ofthe light increases and a light amount to be detected decreases.

From the above results, to obtain the super resolution effect, it isdesirable that the mean particle diameter of the precipitated particleslies within a range from 1 nm or more to 70 nm or less. To obtain thehigher super resolution effect, it is desirable that the particlediameter of the fine particles lies within a range from 5 nm or more to50 nm or less.

If the discontinuous phases surrounding the particles do not existeither, no super resolution effect is derived. Even if the film isconstructed only by the perfect amorphous phases, no super resolutioneffect is derived. By the above examination, the relation between thethickness of continuous phases existing between the particles and thesuper resolution effect is checked, so that the high super resolutioneffect is not obtained if the width of continuous phase between theparticles is less than 0.3 nm. It has been found that, when thecontinuous phase width lies within a range from 0.3 nm or larger to 100nm or less, the super resolution effect can be obtained. Thus, it hasbeen found that, when the continuous phase width increases and theparticle diameter of the fine particles relatively decreases, it iscontrarily difficult to obtain the super resolution effect.

From the above results, although the continuous phases have to exist, itis desirable that the continuous phase width lies within a range from0.3 nm or more to 100 nm or less.

If the continuous phases are an insulating substance (dielectricsubstance) of inorganic materials having a wide band gap, excellenttranslucent performance is obtained and a sufficient reflectionintensity is obtained. Further, when the continuous phases are amorphousinorganic compounds, further better translucent performance is obtained.If the continuous phases are a dielectric substance, the fine particlesas discontinuous phases do not disperse the light even if they are asemiconductor or metal so long as the particle diameter is sufficientlysmaller than a wavelength of laser to be used, specifically speaking, solong as it is equal to or shorter than {fraction (1/10)} of a wavelengthto be used for measurement. The light is influenced by a dipole ofelectrons which are excited in the fine particles by the light energyand the super resolution effect can be obtained.

Even in the case where the formed fine particles are inorganic compoundsof an insulating substance as mentioned in the embodiment, if anexciting state is formed because electrons in the compounds are excitedby the light and the refractive index or the like of the film ischanged, the super resolution effect can be obtained.

The above embodiment has been mentioned with respect to the case wherethe laser wavelength is set to 650 nm and with respect to the systemcontaining Co. However, it has been found that, according to this Cooxide, good super resolution characteristics can be obtained in almostthe whole band of the visible light. It has been found that a similareffect can be obtained also in the case where V, Cr, Mn, Fe, or Ni asanother transition metal element is allowed to be contained.

Embodiment 3

An RAM disk constructed by forming the film examined as mentioned aboveonto the board is subsequently formed and its characteristics areevaluated. FIG. 8 is a diagram showing a partial cross section of theRAM disk formed in the embodiment. In FIG. 8, reference numeral 1denotes the board, 2 the super resolution film, 3 the recording film, 4the reflecting film, and 5 and 85 protecting films. An arrow in thediagram indicates an entering direction of light (for example, laserbeam) for recording or reproduction. In the embodiment, a disk-shapedboard having a thickness of 0.6 mm and a diameter of 120 mm is used as apolycarbonate board of the board 1. The super resolution film 2 having athickness of 300 nm is formed on the board 1 by a sputtering method. AZnS—SiO₂ protecting film having a thickness of 80 nm is formed on thefilm 2. After that, a Ge—Sb—Te system phase change film serving as arecording film having a thickness of about 20 nm is likewise formed bythe sputtering method. After the formation of the protecting film ofabout 90 nm, an AlTi reflecting film having a thickness of about 200 nmis further formed. In a manner similar to the case of the ROM disk, twoboards on each of which the films shown in FIG. 8 have been formed areadhered to each other with a UV curable resin in a state where thereflecting films 4 are set to the back side, thereby obtaining a desiredRAM disk.

In the embodiment, the film having the same compositions as those in thefilm of No. 4 in Table 1 is used as a super resolution film. An RAM diskon which no super resolution film is formed is also formed as acomparison example.

FIG. 9 shows a reproduction output intensity of the RAM disk on whichrecording marks having the same shape have been formed at regularintervals for a mark length of the recording marks. A reading laserpower is set to 2 mW. It has been found that the reproduction output inthe case where the super resolution film having the same compositions asthose in the film of No. 4 has been formed is higher than that of thecomparison example in which no super resolution film is formed (withoutsuper resolution film in FIG. 9) with respect to a short mark length. Ithas, therefore, been found that in the case where the super resolutionfilm has been formed, the output can be reproduced with respect to theshorter mark length. From this result, the super resolution effect canbe confirmed also for the RAM disk.

By examining all of the super resolution films in Table 1, resultssimilar to those in case of the ROM disk are obtained.

Subsequently, a space intensity distribution of the reflection lightwhen the above super resolution effect has been obtained is examined.FIG. 10 shows a diagram of intensity distributions of the laser beam forthe progressing direction of the beam in the case where the film hasbeen formed and the super resolution effect has been obtained and thecase where no super resolution film is formed. The intensitydistribution upon entering shows a Gaussian distribution. It has beenfound that, when no super resolution film is formed, a spacedistribution intensity 101 of the reflection light almost shows theGaussian distribution, and that when the super resolution film isformed, a space distribution intensity 102 of the reflection light showsa state where the distribution of the beam is deviated in theprogressing direction. At the same time, it has been found that a beamdiameter Q′ at a beam intensity necessary to read out is smaller than abeam diameter Q necessary to read out in the case where no superresolution film is formed.

As mentioned above, by forming the super resolution film according tothe embodiment, the intensity or intensity distribution of the readinglight can be changed. The super resolution effect can be obtained insuch a case.

Subsequently, wavelength dependence of the super resolution effect isexamined. The wavelength dependence is examined by a method whereby anRAM disk similar to that of FIG. 8 is formed, an output for the marklength similar to that in FIG. 9 is obtained with respect to eachwavelength, and the minimum value (1 m) of the mark length at which theoutput is equal to or larger than 30 dB is examined. Lasers of 410 nm(blue), 520 nm (green), and 650 nm (red) are used as laser beams.

Results are shown in Table 2. In case of any of films, it has been foundthat the minimum value 1 m of the mark length at which the read outputis equal to or larger than 30 dB decreases as the wavelength is shorter.This is because, in case of using the same optical lens, the shorter thewavelength is, the smaller the converged spot diameter is, and even asmall mark can be reproduced.

TABLE 2 1m (μm) No. 410 nm 520 nm 650 nm 4 0.19 0.24 0.30 5 0.19 0.240.30 6 0.17 0.22 0.28 7 0.17 0.22 0.28 10 0.19 0.24 0.30 11 0.19 0.240.30 12 0.17 0.22 0.28 15 0.19 0.24 0.30 16 0.19 0.24 0.30 17 0.19 0.240.30 19 0.19 0.24 0.30 20 0.19 0.24 0.30 21 0.19 0.24 0.30 22 0.21 0.260.32 23 0.19 0.24 0.30 24 0.17 0.22 0.28 25 0.17 0.22 0.28 26 0.21 0.260.32 27 0.19 0.24 0.30 28 0.19 0.24 0.30 29 0.19 0.24 0.30 30 0.25 0.320.40

With respect to the RAM disk on which the film by which the superresolution effect was obtained in Table 1 has been formed, it has beenfound that the minimum value 1 (μm) of the mark length is small at anyof the wavelengths. It has, consequently, been found that by forming thefilm, the readable mark length can be reduced multiplicatively by boththe realization of the short laser wavelength and the super resolutioneffect.

Embodiment 4

Deterioration of the film for the repetitive reproduction issubsequently examined. Evaluation is performed by repetitivelyirradiating the reproduction signal light to the formed RAM disk anddetecting its reproduction output. A mark length of the recording marksis set to 0.3 μm. A film having the same compositions as those in thefilm of No. 4 in Table 1 is used as a super resolution film. Further, aphthalocyanine system organic film is selected as a comparison exampleand is similarly examined.

FIG. 11 shows an output for the number of repeating times. In case ofthe disk on which the phthalocyanine system organic film has beenformed, it has been found that the output gradually decreases from apoint corresponding to the number of repeating times that is slightlysmaller than 10,000 times. In case of the disk on which a glass filmconstructed by inorganic compounds having the same compositions as thosein the film of No. 4 in Table 1 according to the embodiment has beenformed, the output hardly decreases even by the repetitive reproductionof 100,000 times. As mentioned above, according to the optical disk ofthe embodiment, it has been found that the super resolution effect isheld even after completion of the repetitive reproduction.

A high stability can be obtained for the repetitive reproduction even inthe case where the films by which the super resolution effect has beenderived in the embodiment 2 (in Table 1, Nos. 5 to 7, Nos. 10 to 12,Nos. 15 to 17, Nos. 19 to 29) among the other glass films in Table 1 areused as glass films.

As shown above, according to the embodiment, a read only optical disk(ROM disk) of a large capacity in which, further, a degree ofdeterioration is small for the repetitive reading operation is obtained.A large capacity rewritable optical disk (RAM disk) in which adeterioration is small for the repetitive reading and writing operationsis obtained. Further, according to the embodiment, since an oxide suchas transition metal or the like is contained in the glass board, a largecapacity read only optical disk (ROM disk) can be obtained by themanufacturing based on the ordinary optical disk manufacturing steps.According to the embodiment, a large capacity rewritable optical disk(RAM disk) can be obtained by the manufacturing based on the ordinaryoptical disk manufacturing steps.

According to the invention, an optical recording medium having the superresolution film in which an output deterioration is small even if thereproduction is repetitively performed or the recording and reproductionare repetitively performed can be obtained.

According to the invention, an optical recording medium having the superresolution film in which good productivity is obtained and which has thesuper resolution effect can be obtained.

INDUSTRIAL APPLICABILITY

The optical information recording medium according to the invention isgenerally called an optical disk and, particularly, a super resolutionfilm which can be used as an optical disk on/from which information canbe recorded/reproduced and can record/reproduce information at a highdensity and has the high super resolution effect can be provided.

What is claimed is:
 1. An optical information recording mediumcomprising, at least: a board on which pits having information have beenformed; and a film which is formed directly on said board or formedthereon through another layer and changes a reflectance or an intensitydistribution of reflection light in dependence on an intensity ofincident light, wherein said film is inorganic compounds constructed byN (N is an integer of 2 or more) kinds of phases, the phases in a rangefrom at least one kind to (N−1) kinds among said N kinds of phases arecontinuous phases, and the other phases are discontinuous phases.
 2. Anoptical information recording medium comprising, at least: a board; afilm which is formed directly on said board or formed thereon throughanother layer and changes a reflectance or an intensity distribution ofreflection light in dependence on an intensity of incident light; and arecording film which is formed directly on said film or formed thereonthrough another layer and on which information is recorded by the light,wherein said film is inorganic compounds constructed by N (N is aninteger of 2 or more) kinds of phases, the phases in a range from atleast one kind to (N−1) kinds among said N kinds of phases arecontinuous phases, and the other phases are discontinuous phases.
 3. Amedium according to claim 1 or 2, wherein a mean diameter of saiddiscontinuous phases lies within a range from 1 nm or larger to 70 nm orless and a width of continuous phases existing between saiddiscontinuous phases lies within a range from 0.3 nm or larger to 100 nmor less.
 4. A medium according to any one of claims 1 and 2, whereinsaid continuous phases are amorphous inorganic compounds and saiddiscontinuous phases are crystal inorganic compounds.
 5. A mediumaccording to any one of claims 1 and 2, wherein said continuous phasesare a dielectric substance and said discontinuous phases are any of ametal, a semiconductor, and a dielectric substance.
 6. An opticalinformation recording/reproducing apparatus comprising, at least: lasersof a plurality of wavelengths; means for selecting one of said lasers;and a focus adjusting unit for adjusting a focal point which changesevery laser, wherein said apparatus further has means for discriminatinga recording capacity of an optical information recording medium torecord or reproduce according to any one of claims 1 and 2 and means forchanging a tracking in accordance with the medium discriminated by saiddiscriminating means.
 7. An optical information recording/reproducingapparatus according to claim 6, wherein a mean diameter of saiddiscontinuous phases lies within a range from 1 nm or larger to 70 nm orless and a width of continuous phases existing between saiddiscontinuous phases lies within a range from 0.3 nm or larger to 100 nmor less.
 8. An optical information recording/reproducing apparatusaccording to claim 6, wherein said continuous phases are amorphousinorganic compounds and said discontinuous phases are crystal inorganiccompounds.
 9. An optical information recording/reproducing apparatusaccording to claim 6, wherein said continuous phases are a dielectricsubstance and said discontinuous phases are any of a metal, asemiconductor, and a dielectric substance.
 10. An optical informationrecording medium comprising, at least: a board on which pits havinginformation have been formed; and a film which is formed directly onsaid board or formed thereon through another layer and changes areflectance or an intensity distribution of reflection light independence on an intensity of incident light, wherein said film isconstructed by N (N is an integer of 2 or more) kinds of phasescontaining at least one or more kinds of elements selected from Co, Ti,V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a range from atleast one kind to (N−1) kinds among said phases are continuous phases,and the other phases are discontinuous phases.
 11. An opticalinformation recording medium comprising, at least: a board; a film whichis formed directly on said board or formed thereon through another layerand changes a reflectance or an intensity distribution of reflectionlight in dependence on an intensity of incident light; and a recordingfilm which is formed directly on said film or formed thereon throughanother layer and on which information is recorded by the light, whereinsaid film is constructed by N (N is an integer of 2 or more) kinds ofphases containing at least one or more kinds of elements selected fromCo, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a rangefrom at least one kind to (N−1) kinds among said N kinds of phases arecontinuous phases, and the other phases are discontinuous phases.
 12. Anoptical information recording medium comprising, at least: a board; afilm which is formed directly on said board or formed thereon throughanother layer and changes a reflectance or an intensity distribution ofreflection light in dependence on an intensity of incident light; and arecording film which is formed directly on said film or formed thereonthrough another layer and on which information is recorded by the light,wherein a refractive index of said film changes due to said incidentlight when the incident light enters, and assuming that a refractiveindex at the time when no incident light enters is labelled to n₀ and anintensity of the incident light is set to I, if an absolute value n ofthe refractive index that is measured is indicated by n=n₀+n₂I a valueof n₂ lies within a range from 1.0×10⁻⁹ (m²/W) or larger to 1.0×10-7*m²/W) or less.
 13. A medium according to claim 12, wherein the absolutevalue n of said refractive index changes in a time within a range from2.50×10⁻⁷ second or longer to 3.50×10⁻⁷ second or shorter after anirradiation of the incident light and is recovered to an originalrefractive index in a time interval within a range from 2.5×10⁻⁷ secondor longer to 1.0×10⁻² second or shorter after a removal of the incidentlight.
 14. A medium according to any one of claims 10 to 13, whereinsaid film is an oxide which contains a Co oxide and in which a remainingpart is constructed by elements of at least one or more kinds among Si,Ti, Al, Pb, and Bi.
 15. An optical information recording/reproducingapparatus comprising, at least: lasers of a plurality of wavelengths;means for selecting one of said lasers; and a focus adjusting unit foradjusting a focal point which changes every laser, wherein saidapparatus further has means for discriminating a recording capacity ofan optical information recording medium to record or reproduce accordingto any one of claims 10-13 and means for changing a tracking inaccordance with the medium discriminated by said discriminating means.16. An optical information recording/reproducing apparatus according toclaim 15, wherein said film is an oxide which contains a Co oxide and inwhich a remaining part is constructed by elements of at least one ormore kinds among Si, Ti, Al, Pb, and Bi.